The serious fuel leak immediately after t/o (punctured tank from tyre burst and losing fuel rapidly) was the scenario discussed. Admittedly a freak occurrence but it lead to the thought of doing an autoland if the weather at the departure airfield was marginal and the a/c was still above mlw. I should think serious smoke on the flight deck would be another good reason.
The point was really that the a/c was capable of doing more than just what the FCOM indicates in an extreme situation.